During using a wire-cutting electric discharging machine, since the wave width of current waveform in an electric discharging machine is too long (&gt;10 .mu.s), it would cause the breakage of the wire and a coppersticking phenonmenon; therefore, the wave width of current waveform in an electric discharging machine for wire cutting is usually limited within 10 .mu.s. In order to elevate the cutting speed, a considerable higher energy has to be applied in the discharging gap within the aforesaid period of time, i.e., to increase the value of peak current. During discharging, the wire electrode is under high tensile condition, and therefore the wire electrode is often broken as a result of consumption. A triangular discharging waveform can prevent the wire electrode and working piece from fast consumption ratio; in other words, it can increase the cutting speed.